Implantable neuromodulation systems have proven therapeutic in a wide variety of diseases and disorders. Pacemakers and Implantable Cardiac Defibrillators (ICDs) have proven highly effective in the treatment of a number of cardiac conditions (e.g., arrhythmias). Spinal Cord Stimulation (SCS) systems have long been accepted as a therapeutic modality for the treatment of chronic pain syndromes, and the application of tissue stimulation has begun to expand to additional applications such as angina pectoralis and incontinence. Deep Brain Stimulation (DBS) has also been applied therapeutically for well over a decade for the treatment of refractory chronic pain syndromes, and DBS has also recently been applied in additional areas such as movement disorders and epilepsy. Further, in recent investigations, Peripheral Nerve Stimulation (PNS) systems have demonstrated efficacy in the treatment of chronic pain syndromes and incontinence, and a number of additional applications are currently under investigation. Furthermore, Functional Electrical Stimulation (FES) systems, such as the Freehand system by NeuroControl (Cleveland, Ohio), have been applied to restore some functionality to paralyzed extremities in spinal cord injury patients.
Each of these implantable neuromodulation systems typically includes at least one neuromodulation lead implanted at the desired modulation site and an Implantable Pulse Generator (IPG) implanted remotely from the modulation site, but coupled either directly to the neuromodulation lead(s), or indirectly to the neuromodulation lead(s) via one or more lead extensions. Thus, electrical pulses can be delivered from the neuromodulator to the electrodes carried by the neuromodulation lead(s) to stimulate or activate a volume of tissue in accordance with a set of modulation parameters and provide the desired efficacious therapy to the patient. The neuromodulation system may further comprise a handheld remote control (RC) to remotely instruct the neuromodulator to generate electrical modulation pulses in accordance with selected modulation parameters. The RC may, itself, be programmed by a technician attending the patient, for example, by using a Clinician's Programmer (CP), which typically includes a general purpose computer, such as a laptop, with a programming software package installed thereon.
Electrical modulation energy may be delivered from the neuromodulation device to the electrodes in the form of an electrical pulsed waveform. Thus, electrical modulation energy may be controllably delivered to the electrodes to modulate neural tissue. The configuration of electrodes used to deliver electrical pulses to the targeted tissue constitutes an electrode configuration, with the electrodes capable of being selectively programmed to act as anodes (positive), cathodes (negative), or left off (zero). In other words, an electrode configuration represents the polarity being positive, negative, or zero. Other parameters that may be controlled or varied include the amplitude, width, and rate of the electrical pulses provided through the electrode array. Each electrode configuration, along with the electrical pulse parameters, can be referred to as a “modulation parameter set.”
With some neuromodulation systems, and in particular, those with independently controlled current or voltage sources, the distribution of the current to the electrodes (including the case of the neuromodulation device, which may act as an electrode) may be varied such that the current is supplied via numerous different electrode configurations. In different configurations, the electrodes may provide current or voltage in different relative percentages of positive and negative current or voltage to create different electrical current distributions (i.e., fractionalized electrode configurations).
As briefly discussed above, an external control device can be used to instruct the neuromodulation device to generate electrical pulses in accordance with the selected modulation parameters. Typically, the modulation parameters programmed into the neuromodulation device can be adjusted by manipulating controls on the external control device to modify the electrical modulation energy delivered by the neuromodulation device system to the patient. Thus, in accordance with the modulation parameters programmed by the external control device, electrical pulses can be delivered from the neuromodulation device to the electrode(s) to modulate a volume of tissue in accordance with the set of modulation parameters and provide the desired efficacious therapy to the patient. The best modulation parameter set will typically be one that delivers electrical energy to the volume of tissue that must be modulate in order to provide the therapeutic benefit (e.g., treatment of pain), while minimizing the volume of non-target tissue that is modulated.
However, the number of electrodes available combined with the ability to generate a variety of complex electrical pulses, presents a huge selection of modulation parameter sets to the clinician or patient. For example, if the neuromodulation system to be programmed has an array of sixteen electrodes, millions of modulation parameter sets may be available for programming into the neuromodulation system. Today, neuromodulation system may have up to thirty-two electrodes, thereby exponentially increasing the number of modulation parameters sets available for programming.
To facilitate such selection, the clinician generally programs the neuromodulation device through a computerized programming system. This programming system can be a self-contained hardware/software system, or can be defined predominantly by software running on a standard personal computer (PC). The PC or custom hardware may actively control the characteristics of the electrical pulses generated by the neuromodulation device to allow the optimum modulation parameters to be determined based on patient feedback or other means and to subsequently program the neuromodulation device with the optimum modulation parameter set or sets. The computerized programming system may be operated by a clinician attending the patient in several scenarios.
For example, in order to achieve an effective result from conventional SCS, the lead or leads must be placed in a location, such that the electrical modulation (and in this case, electrical modulation) will cause paresthesia. The paresthesia induced by the electrical modulation and perceived by the patient should be located in approximately the same place in the patient's body as the pain that is the target of treatment. If a lead is not correctly positioned, it is possible that the patient will receive little or no benefit from an implanted SCS system. Thus, correct lead placement can mean the difference between effective and ineffective pain therapy. When leads are implanted within the patient, the computerized programming system, in the context of an operating room (OR) mapping procedure, may be used to instruct the neuromodulation device to apply electrical modulation to test placement of the leads and/or electrodes, thereby assuring that the leads and/or electrodes are implanted in effective locations within the patient.
Once the leads are correctly positioned, a fitting procedure, which may be referred to as a navigation session, may be performed using the computerized programming system to program the external control device, and if applicable the neuromodulation device, with a set of modulation parameters that best addresses the painful site. Thus, the navigation session may be used to pinpoint the volume of activation (VOA) or areas correlating to the pain. Such programming ability is particularly advantageous for targeting the tissue during implantation, or after implantation should the leads gradually or unexpectedly move that would otherwise relocate the modulation energy away from the target site. By reprogramming the neuromodulation device (typically by independently varying the modulation energy on the electrodes), the volume of activation (VOA) can often be moved back to the effective pain site without having to re-operate on the patient in order to reposition the lead and its electrode array. When adjusting the volume of activation (VOA) relative to the tissue, it is desirable to make small changes in the proportions of current, so that changes in the spatial recruitment of nerve fibers will be perceived by the patient as being smooth and continuous and to have incremental targeting capability.
Although alternative or artifactual sensations are usually tolerated relative to the sensation of pain, patients sometimes report these sensations to be uncomfortable, and therefore, they can be considered an adverse side-effect to neuromodulation therapy in some cases. Because the perception of paresthesia has been used as an indicator that the applied electrical energy is, in fact, alleviating the pain experienced by the patient, the amplitude of the applied electrical energy is generally adjusted to a level that causes the perception of paresthesia. It has been shown, however, that the delivery of sub-threshold electrical energy (e.g., high-rate pulsed electrical energy and/or low pulse width electrical energy) can be effective in providing neuromodulation therapy for chronic pain without causing paresthesia.
Although sub-threshold modulation therapies have shown good efficacy in early studies, because there is a lack of paresthesia that may otherwise indicate that the neuromodulation therapy is effective, it is difficult to immediately determine if the delivered sub-threshold therapy is optimized in terms of providing efficacious therapy to the patient. Given the lack of paresthesia, the clinician may have to try infinite combinations of electrodes, and modulation parameters of those electrodes to arrive at an optimal sub-threshold therapy program. Thus, identifying an efficacious sub-threshold therapy program may take several days, if not weeks, requiring several reprogramming sessions with the clinicians.
Thus, there remains a need to provide a means to ensure that a patient is being effectively treated using electrical sub-threshold therapy.